The embryonic chick cardiovascular system will be used to further substantiate the possible relationships between alterations in hemodynamics and/or cardiac function and the production of cardiovascular malformations. Catecholamines, compounds which have been shown to induce cardiac and aortic arch anomalies in chick embryos in this laboratory, and methylxanthines, compounds which induce cardiac malformations and aortic aneurysms, will be administered to embryos at stages of embryogenesis which have proven sensitive to these agents. In light of documented intracellular biochemical mechanisms of catecholamines and methylxanthines, calcium, calcium antagonists (verapamil, D-600 and SKF24260), glucose and selected inhibitors of cyclic adenosine 3'5' monophosphate phosphodiesterase (prazosin and papaverine) will be used as probes in this study. Microcinematography, time-lapse microphotography, histology, electron microscopy, bioelectrical impedance cardiography and electrocardiography will be employed in search of valuable clues to one or more mechanisms involved in abnormal cardiogenesis and/or aortic arch teratogenesis.